1. Technical Field
The present invention relates in general to measuring parameters of sliders and disks used in magnetic storage devices and, in particular, to a system, method and apparatus for measuring head-disk clearance by slider vibration and calibrating the fly height performance of sliders in disk drives.
2. Description of the Related Art
In a magnetic disk recording system, a slider containing magnetic transducers for reading and writing magnetic transitions is urged toward the rotating disk by a suspension. As the disk rotates an air bearing develops under the slider and causes it to fly above the disk. The distance between the slider and the disk surface is the clearance. The disk typically includes a thin film overcoat and a set of thin films which include one or more ferromagnetic layers in which information is recorded. A disk drive can contain multiple disks and multiple sliders.
Lower slider fly heights are required for disk drives with higher areal densities. As a result, it is becoming increasingly difficult to measure the actual fly height of sliders. One technique uses white light interferometry and works adequately for large fly heights, but it loses accuracy for smaller fly heights. In addition, it is very sensitive to the optical constants of the slider overcoat. Another technique uses small solid bumps of known height on the disk and measures the acoustic emissions as the slider passes over or hits the bumps. Since it has proved impractical to make very small bumps, this particular technique loses accuracy for very small fly heights. Although this and other methods are workable for some applications, an improvement in measuring head-disk clearance and calibrating the fly height performance of disk drives would be desirable for high performance drive applications.